1. Field of the Invention
The invention is directed to lampholders for electrical lamps, and more particularly to lampholders to mechanically support and provide electrical power to fluorescent lamps.
2. Description of the Prior Art
Originally, fluorescent tube lamps were cylindrical glass enclosures or envelopes which contained an ionizable gas. A tungsten filament located at each of the two tube ends required a low voltage from a ballast or "starter" to heat the filament to incandescence to create thermionic emissions so that enough ions were created to ionize the gas. The voltage from the ballast was applied to the filaments via two metallic lamp pins which extended out of each end of the glass tube envelope. The two lamp pins at each end were engaged by lampholders at each end which provided mechanical support and electrical power to the fluorescent lamps.
Later, fluorescent lamps called "cold cathode" lamps were developed that eliminated the need to heat the filament. Instead, a voltage, in the order of 1300 volts, produced by a high-voltage ballast, was applied to the filament to force a sufficient number of tungsten ions from the filament to ionize the gas for ignition However, since the pins also serve with the lampholders as mechanical supports for the fluorescent lamp, and in view of the large number of installed double-contact fluorescent lampholders, a need for fluorescent lamps with two lamp pins at each end continues to exist. Some manufacturers applied an electrical shunt across the two lamp pins at each lamp end, in the belief that the high energizing voltage would need to be evenly distributed across each of the filaments to cause an even dispersion of ions.
FIGS. 1 and 2 show a prior art fluorescent lampholder 10 and the manner in which it was connected to an electrical source. A body 12 fabricated of phenolic, rubber or a suitable plastic is arranged to be placed in a housing, at the ends of a reflector or other similar mounting (not shown). Body 12 has a channel 14 with an entry slot 16 leading from outside body 12 into channel 14. Placed in the open back of body 12 are two lamp pin contacts 18 each intended to engage one of the fluorescent tube pins (not shown) in their notches 22 in the upper portion 20 of lamp pin contacts 18. The lamp pin contacts 18 are assembled to the interior wall of body 12 by fasteners (not shown) extending through an aperture 24 in each of the lamp pin contacts 18. A shunt bar 26 is coupled between the lamp pin contacts 18. The bottom portion 28 of lamp pin contacts 18 are bifurcated as at 30 and provide two coupling tongues 32 which make contact with the bared end of an insulated conductor (not shown). Tongues 32 act as one-way clutches allowing the conductor ends to be inserted but not withdrawn while making electrical contact with such bare conductor ends. A cover 34 of insulating material covers the back of the body 12 and is held in place by a staple 36.
A ballast 40, coupled to the lines 38 from a 120 Volt AC supply 37 at one end, is coupled to shunt 26A which spans lamp pin contacts 18A, 18B and shunt 26B which spans lamp pin contacts 18C, 18D as shown in FIG. 2. Within the fluorescent lamp 42 tube, at one end thereof is a filament 44 connected across lamp pin contacts 18A, 18B and at the other end is a filament 46 connected across lamp pin contacts 18C, 18D.
To use the lampholder 10, a fluorescent lamp (not shown) would be turned so that its lamp pins at one end are positioned one above the other and the lamp pins made to enter slot 16 and moved towards the bottom of body 12. Once the lamp pins are aligned with the channel 14, the lamp is rotated until each of the lamp pins enters the notch 22 of its associated lamp pin contact 18. The tapered lead-ins to each of the notches 22 from above and below assure that the lamp pins enter the notches 22. The resilience and shape of the portion 20 allows the portion 20 to be deflected as the lamp pins move into position in the notches 22 and return to grip the lamp pins once they are in their associated notches 22. A similar lampholder 10 is positioned at the opposite end of the lamp to engage the lamp pins thereat.
With further improvements to the lamp and electronic ballast no filament is needed. Currently, fluorescent lamps are manufactured to work in either a hot cathode mode or a cold cathode mode.